The field of the invention is in the interferometer art, and more particularly, that of an interferometer-type device for measuring the velocity of a moving reflective surface through the Doppler shifts of reflected laser beams.
Velocity measuring devices utilizing reflected laser beams are known. Leslie E. Drain in his paper, "Doppler Velocimetry," in Laser Focus for October 1980, pages 68-73, discusses various types of laser interferometers including heterodyne, fringe crossing, and differential Doppler concepts. U.S. Pat. No. 3,432,237 entitled VELOCITY MEASURING DEVICE, to patentees Flower and Gamertsfelder, discloses a velocity measuring device utilizing the signal generated by the passing of successive reflected lobes of a laser beam by an aperture. The paper "Laser Velocimeter" published in IEEE Conference Record of 1969 Fourth Annual Meeting of the IEEE Industry and General Applications Group, Oct. 12-16, 1969, at pages 307-314, by R. A. Flower, and the paper "A Laser Velocimeter" by Gus Stavis, published in TNB Volume 8, No. 4, 1965, by GPL Division of General Precision Incorporated, further discusses velocimeters utilizing the passing of side lobes of reflected laser beams by an aperture. A commercially available laser Doppler velocimeter is described in the brochure "Laser Doppler Velocimeter" by Cambridge Physical Sciences, available through U.K. agents: Survey and General Instrument Company Ltd., Fircroft Way, Edenbridge, Kent, U.K. Further background information on optical heterodyning may be found in the paper "The Antenna Properties of Optical Heterodyne Receivers" by A. E. Siegman, published in Proceedings of the IEEE for October 1966, at pages 1350-1356.